Coated cutting tool

ABSTRACT

A coated cutting tool includes a substrate and a coating. The coating has an α-Al 2 O 3 -multilayer of alternating sublayers of α-Al 2 O 3  and sublayers of TiCO, TiCNO, AlTiCO or AlTiCNO. The α-Al 2 O 3 -multilayer includes at least 5 sublayers of α-Al 2 O 3 , wherein the total thickness of the α-Al 2 O 3 -multilayer is 1-15 μm and wherein a period in the α-Al 2 O 3 -multilayer is 50-900 nm. The α-Al 2 O 3 -multilayer exhibits an XRD diffraction over a θ-2θ scan of 20°-140°, wherein the relation of the intensity of the 0 0 12 diffraction peak (peak area), I(0 0 12), to the intensities of the 1 1 3 diffraction peak (peak area), I(1 1 3), the 1 1 6 diffraction peak (peak area), I(1 1 6), and the 0 2 4 diffraction peak (peak area), I(0 2 4), is I(0 0 12)/I(1 1 3)&gt;1, I(0 0 12)/I(1 1 6)&gt;1 and I(0 0 12)/I(0 2 4)&gt;1.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a coated cutting tool comprising anα-Al₂O₃-multilayer consisting of alternating sublayers of α-Al₂O₃ andsublayers of TiCO, TiCNO, AlTiCO or AlTiCNO, said α-Al₂O₃-multilayercomprises at least 5 sublayers of α-Al₂O₃, wherein the total thicknessof said α-Al₂O₃-multilayer is 1-15 μm and wherein the period in theα-Al₂O₃-multilayer is 50-900 nm.

BACKGROUND

In the metal cutting industry coated cutting tools are well known in theart. CVD coated cutting tools and PVD coated cutting tools are the twomost dominating types of coated cutting tools. Advantages with thesecoatings are high resistance to chemical and abrasive wear which areimportant to achieve long tool life of the coated cutting tool.

CVD coatings comprising a layer of TiCN together with a layer of aluminaare known to perform well in for example turning in steel. Multilayersof alumina are for example known from U.S. Pat. No. 9,365,925 B2disclosing sublayers of alumina separated by a bonding layer comprisingboth a layer of TiCN and a layer of TiAlOC.

There is a continuous need of finding cutting tool coatings that canprolong the life time of the cutting tool and/or that can withstandhigher cutting speeds than the known cutting tool coatings.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a wear resistantcoating with improved properties in metal cutting tool applications. Itis a further object to provide a wear resistant coating that provides ahigh crater and flank wear resistance in combination with a high flakingresistance in turning of steel and hardened steel. A further object ofthe invention is to provide a coating with a combined high crater wearresistance with a high resistance against flaking due to plasticdeformation of the cutting edge.

At least one of these objects is achieved with a cutting tool accordingto claim 1.

Preferred embodiments are listed in the dependent claims.

The present disclosure relates to a coated cutting tool comprising asubstrate and a coating, wherein the coating comprises anα-Al₂O₃-multilayer consisting of alternating sublayers of α-Al₂O₃ andsublayers of TiCO, TiCNO, AlTiCO or AlTiCNO, said α-Al₂O₃-multilayercomprises at least 5 sublayers of α-Al₂O₃, wherein the total thicknessof said α-Al₂O₃-multilayer is 1-15 μm and wherein a period in theα-Al₂O₃-multilayer is 50-900 nm. The α-Al₂O₃-multilayer exhibits an XRDdiffraction over a θ-2θ scan of 20°-140°, wherein the relation of theintensity of the 0 0 12 diffraction peak (peak area), I(0 0 12), to theintensities of the 1 1 3 diffraction peak (peak area), I(1 1 3), the 1 16 diffraction peak (peak area), I(1 1 6), and the 0 2 4 diffraction peak(peak area), I(0 2 4), is I(0 0 12)/I(1 1 3)>1, I(0 0 12)/I(1 1 6)>1 andI(0 0 12)/I(0 2 4)>1. In one embodiment the ratio I(0 0 12)/I(1 1 3) ispreferably >2, more preferably >3, even more preferably >4. In oneembodiment the ratio I(0 0 12)/I(0 2 4) is preferably >2, morepreferably >3. No thin film correction is applied to the diffractiondata but the data is treated with Cu—K_(α2) stripping and backgroundfitting as disclosed in more detail below.

It has surprisingly been found that a coated cutting tool provided witha α-Al₂O₃-multilayer in a coating according to the invention canwithstand flaking of the coating due to plastic deformation of thecutting edge in turning operations in steel and hardened steel. Thishighly orientated α-Al₂O₃-multilayer of the present invention providesboth a high crater wear resistance and a high resistance againstflaking.

In one embodiment of the present invention the intensity of the 0 1 14diffraction peak (peak area), I(0 1 14), to the intensity of the 0 0 12diffraction peak (peak area), I(0 0 12), is I(0 1 14)/I(0 0 12)<2,preferably <1, more preferably <0.8 or <0.7.

In one embodiment of the present invention the relation of the intensityof the 1 1 0 diffraction peak (peak area), I(1 1 0), to the intensitiesof the 1 1 3 diffraction peak (peak area), I(1 1 3), and the 0 2 4diffraction peak (peak area), I(0 2 4), is I(110)>each of I(113) andI(024).

In one embodiment of the present invention the relation of the intensityof the 0 0 12 diffraction peak (peak area), I(0 0 12), to the intensityof the 1 1 0 diffraction peak (peak area), I(1 1 0), is I(0 012)>I(110).

In one embodiment of the present invention the TiCO, TiCNO, AlTiCO orAlTiCNO sublayer comprises protrusions, wherein the protrusions arecrystalline.

In one embodiment of the present invention said protrusions comprise atleast one twin boundary, preferably the protrusions share a (111) planeand are extended in its <211> direction. In one embodiment the crystalstructure of said protrusions are cubic.

In one embodiment of the present invention the length of saidprotrusions in its extended direction is 10-100 nm.

In one embodiment of the present invention the height of saidprotrusions as measured in a direction perpendicular to the surfacenormal of the substrate is less than a period of the multilayer,preferably less than 80% of the period of the multilayer, morepreferably less than or equal to 50% of the period of the multilayer.

The protrusions are considered to be important for the adhesion betweenthe sublayers of the α-Al₂O₃-multilayer. A good adhesion is necessary towithstand the high wear during cutting operations.

A high orientation throughout the α-Al₂O₃-multilayer is consideredimportant to provide the high flank and crater wear resistance. The highdegree of orientation of one α-Al₂O₃-sublayer of the α-Al₂O₃-multilayeris continued through a TiCO, TiCNO, AlTiCO or AlTiCNO sublayer.

The average height of said protrusions is preferably less than a periodof the α-Al₂O₃-multilayer. The wear resistance of the α-Al₂O₃-multilayerwill decrease if the α-Al₂O₃-sublayer is not continuous.

In one embodiment of the present invention the average thickness of saidα-Al₂O₃ sublayer is 40-800 nm, preferably 80-700 nm, more preferably100-500 nm or 100-300 nm. The α-Al₂O₃ sublayer should be of a sufficientthickness to provide a high wear resistance but small enough to providethe advantages of a multilayer. If the α-Al₂O₃ sublayer is of a toolarge thickness it will appear as a single layer without the advantagesof being a multilayer. The α-Al₂O₃-multilayer of the present inventionprovides a higher resistance against flaking at plastic deformation ofthe cutting edge and a higher resistance to plastic deformation of thecutting edge as compared to a coating with a single α-Al₂O₃-layer.

In one embodiment of the present invention the coated cutting toolcomprises a first α-Al₂O₃-layer located between the substrate and theα-Al₂O₃-multilayer, wherein the thickness of said first α-Al₂O₃-layer is<1 μm, preferably <0.5 μm, more preferably <0.3 μm or 100-300 nm. It hasbeen found that the first α-Al₂O₃-layer located between the substrateand the α-Al₂O₃-multilayer is important to provide a high resistanceagainst flaking at plastic deformation of the cutting edge. In oneembodiment the first α-Al₂O₃-layer is of the same thickness as one ofthe α-Al₂O₃-sublayers of the α-Al₂O₃-multilayer.

In one embodiment of the present invention the coated cutting toolcomprises at least one layer of TiC, TiN, TiAlN or TiCN located betweenthe substrate and the α-Al₂O₃-multilayer, preferably TiCN. In oneembodiment of the present invention the thickness of the TiC, TiN, TiAlNor TiCN layer is 2-15 μm.

In one embodiment of the present invention the outermost layer of thecoating is an α-Al₂O₃ layer. Alternatively, one or more further layerscan cover the α-Al₂O₃ layer, such as layers of TiN, TiC, Al₂O₃ and/orcombinations thereof. In one embodiment of the present invention saidone or more further layers covering the α-Al₂O₃ layer is/are removedfrom the flank face or the rake face or the cutting edge or combinationsthereof.

In one embodiment of the present invention the substrate is of cementedcarbide, cermet, ceramic, high speed steel or cBN. The substrate shouldhave hardness and toughness that suit the coating of the presentinvention.

In one embodiment of the present invention the substrate is of cementedcarbide comprising 3-14 wt % Co and more than 50 wt % WC. In oneembodiment of the present invention the substrate of the coated cuttingtool consists of cemented carbide comprising 4-12 wt % Co, preferably6-8 wt % Co, optionally 0.1-10 wt % cubic carbides, nitrides orcarbonitrides of metals from groups IVb, Vb and VIb of the periodictable, preferably Ti, Nb, Ta or combinations thereof, and balance WC.

Still other objects and features of the present invention will becomeapparent from the following detailed description considered inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a Scanning Electron Microscope (SEM) image of a fracturedcross section of the coating of sample Multi A24. The columnar TiCNlayer is visible below the α-Al₂O₃-multilayer.

FIG. 2 is a Scanning Electron Microscope (SEM) image of a fracturedcross section of the α-Al₂O₃-multilayer of sample Multi A24. The 1 μmα-Al₂O₃-layer is visible below the α-Al₂O₃-multilayer.

FIG. 3 is a Scanning Electron Microscope (SEM) image of a fracturedcross section of the coating of sample Multi A32. The 1 μm α-Al₂O₃-layeris visible below the α-Al₂O₃-multilayer.

FIG. 4 is a Scanning Electron Microscope (SEM) image of a polished crosssection of the α-Al₂O₃-multilayer of sample Multi A28u.

FIG. 5 is a Scanning Electron Microscope (SEM) image of a fracturedcross section of the sample Multi A40u.

FIG. 6 is a Scanning Electron Microscope (SEM) image of a fracturedcross section of the coating of sample Multi B38.

FIG. 7 is a Scanning Electron Microscope (SEM) image of a polished crosssection of the α-Al₂O₃-multilayer of sample Multi B38. The 1 μmα-Al₂O₃-layer is visible below the α-Al₂O₃-multilayer.

FIG. 8 is a Bright Field Scanning Transmission Electron Microscope(STEM) image of a cross section of a TiCO sublayer between twoα-Al₂O₃-sublayers.

FIG. 9 is a HAADF Scanning Transmission Electron Microscope (HAADF STEM)image of a cross section of a portion of the α-Al₂O₃-multilayer of thecoating of sample Multi A32.

FIG. 10 is a HAADF Scanning Transmission Electron Microscope (HAADFSTEM) image of a cross section of a protrusion of the TiCO sub layer ofthe coating of sample Multi A32. The 111 plane and the 112 plane areindicated with lines in the figure. View is aligned along the 011 zoneaxis.

FIG. 11 is a HAADF Scanning Transmission Electron Microscope (HAADFSTEM) image of a cross section of a protrusion of the TiCO sub layer ofthe coating of sample Multi A32. The 111 plane and the 112 plane areindicated with lines in the figure. View is aligned along the 011 zoneaxis.

FIG. 12 is a XRD diffractogram of sample Multi A28u. No corrections aremade to the intensity data and no Cu—K_(α2) stripping applied. The peaks110, 113, 024, 116, 0 0 12 and 0 1 14 originating from Al₂O₃ areindicated in the figure.

FIG. 13 is a XRD diffractogram of sample Single A1. No corrections aremade to the intensity data and no Cu—K_(α2) stripping applied. The peaks110, 113, 024, 116, 0 0 12 and 0 1 14 originating from Al₂O₃ areindicated in the figure.

DEFINITIONS

The abbreviation “cutting tool” is herein intended to denote cuttingtool inserts, end mills or drills. The application areas are metalcutting applications and can for example be turning, milling ordrilling.

Methods

XRD Analysis

In order to investigate the texture or orientation of the layer(s) X-raydiffraction (XRD) was conducted on the flank face using a PANalyticalCubiX3 diffractometer equipped with a PIXcel detector. The coatedcutting tools were mounted in sample holders to ensure that the flankface of the samples are parallel to the reference surface of the sampleholder and also that the flank face is at appropriate height. Cu-Kαradiation was used for the measurements, with a voltage of 45 kV and acurrent of 40 mA. Anti-scatter slit of ½ degree and divergence slit of ¼degree were used. The diffracted intensity from the coated cutting toolwas measured in the range 20° to 140° 2θ, i.e. over an incident angle θrange from 10 to 70°. The data analysis, including background fitting,Cu—K_(α2) stripping and profile fitting of the data, was done usingPANalytical's X'Pert HighScore Plus software. The output (integratedpeak areas for the profile fitted curve) from this program was then usedto define the coating of the present invention in terms of intensityratios and/or relations.

Normally a so called thin film correction is to be applied to theintegrated peak area data to compensate for differences in intensitiesdue to absorption and different path lengths in layers, but since theTiCO, TiCNO, AlTiCO or AlTiCNO sublayer of the present inventioncomprise protrusions the thickness of this layer is not trivial to setand the path length through this layer is complex. The orientation ofthe multilayer is therefore set based on data without thin filmcorrection applied to the extracted integrated peak area intensities forthe profile fitted curve. Cu—K_(α2) stripping is however applied to thedata before the intensity areas are calculated.

Since possible further layers above the α-Al₂O₃-multilayer will affectthe X-ray intensities entering the α-Al₂O₃-multilayer and exiting thewhole coating, corrections need to be made for these, taken into accountthe linear absorption coefficient for the respective compound in alayer. Alternatively, a further layer, above the α-Al₂O₃-multilayer canbe removed by a method that does not substantially influence the XRDmeasurement results, e.g. chemical etching.

It is to be noted that peak overlap is a phenomenon that can occur inX-ray diffraction analysis of coatings comprising for example severalcrystalline layers and/or that are deposited on a substrate comprisingcrystalline phases, and this has to be considered and compensated for bythe skilled person. A peak overlap of peaks from the α-Al₂O₃ layer withpeaks from the TiCN layer might influence measurement and needs to beconsidered. It is also to be noted that for example WC in the substratecan have diffraction peaks close to the relevant peaks of the presentinvention.

STEM Analysis

In order to investigate the protrusions of the sublayer, STEM analysiswas made in a monochromated, aberration probe corrected Titan 80-300TEM/STEM.

To prepare a specimen of a sample for STEM analysis a dual focused ionbeam system was used, FEI VERSA3D LoVac (Versa). A Pt strip wasdeposited on the surface of the sample, a specimen was cut out into thesample using ion beam. An omniprobe was welded to the PT strip,thereafter the specimen was cut free from the sample and welded to asupport grid made of copper. The specimen was thereafter thinned downusing the ion beam to a thickness of 80-100 nm. A voltage of 30 kV andthree different currents were used for thinning down the specimen. Acurrent of 1 nA was used to thin down the sample to around 400 nmthickness. The specimen was tilted ±2 degrees relative the ion beamduring thinning. A current of 0.3 nA was used to thin down the sample toaround 200 nm thickness. The specimen was tilted ±1.5 degrees relativethe ion beam during thinning. A current of 0.1 nA was used to thin downthe sample to around 100 nm thickness. The specimen was tilted ±1.2degrees relative the ion beam during thinning. After thinning down thespecimen to around 100 nm the sides of the specimen were cleaned usinglow kV ions to remove amorphous material. The first cleaning step wasdone using a voltage of 5 kV and a current of 48 pA. The specimen wasinclined ±5 degrees relative the ion beam during cleaning and each sidewas cleaned for 2 minutes. The second cleaning step was done using avoltage of 2 kV and a current of 27 pA. The specimen was inclined ±7degrees relative the ion beam during cleaning and each side was cleanedfor 30 seconds.

The analyse of the protrusions can be done using HAADF STEM. In theanalyse of the protrusions an initial step is to align the protrusionsbased on their respective Kikuchi pattern. The crystal structure of theprotrusions is handled as cubic (see for example PDF 00-050-0681 forTiCNO) and each protrusion is to be oriented along a known zone axis,such as its 011 zone axis, before conclusions about the crystallographicextension of the protrusions is to be drawn. The orientation of the twinboundary can then be identified as well as the direction of theextension of the protrusion by Fourier transforms of the data (fastFourier transform).

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure relates to a coated cutting tool comprising asubstrate and a coating, wherein the coating comprises anα-Al₂O₃-multilayer consisting of alternating sublayers of α-Al₂O₃ andsublayers of TiCO, TiCNO, AlTiCO or AlTiCNO, said α-Al₂O₃-multilayercomprises at least 5 sublayers of α-Al₂O₃, wherein the total thicknessof said α-Al₂O₃-multilayer is 1-15 μm and wherein a period in theα-Al₂O₃-multilayer is 50-900 nm. The α-Al₂O₃-multilayer exhibits an XRDdiffraction over a θ-2θ scan of 20°-140°, wherein the relation of theintensity of the 0 0 12 diffraction peak (peak area), I(0 0 12), to theintensities of the 1 1 3 diffraction peak (peak area), I(1 1 3), the 1 16 diffraction peak (peak area), I(1 1 6), and the 0 2 4 diffraction peak(peak area), I(0 2 4), is I(0 0 12)/I(1 1 3)>1, I(0 0 12)/I(1 1 6)>1 andI(0 0 12)/I(0 2 4)>1. In one embodiment the ratio I(0 0 12)/I(1 1 3) ispreferably >2, more preferably >3, even more preferably >4. In oneembodiment the ratio I(0 0 12)/I(0 2 4) is preferably >2, morepreferably >3. No thin film correction is applied to the diffractiondata but the data is treated with Cu—K_(α2) stripping and backgroundfitting as disclosed in more detail below.

It has surprisingly been found that a coated cutting tool provided witha α-Al₂O₃-multilayer in a coating according to the invention canwithstand flaking of the coating due to plastic deformation of thecutting edge in turning operations in steel and hardened steel. Thishighly orientated α-Al₂O₃-multilayer of the present invention providesboth a high crater wear resistance and a high resistance againstflaking.

In one embodiment of the present invention the intensity of the 0 1 14diffraction peak (peak area), I(0 1 14), to the intensity of the 0 0 12diffraction peak (peak area), I(0 0 12), is I(0 1 14)/I(0 0 12)<2,preferably <1, more preferably <0.8 or <0.7.

In one embodiment of the present invention the relation of the intensityof the 1 1 0 diffraction peak (peak area), I(1 1 0), to the intensitiesof the 1 1 3 diffraction peak (peak area), I(1 1 3), and the 0 2 4diffraction peak (peak area), I(0 2 4), is I(110)>each of I(113) andI(024).

In one embodiment of the present invention the relation of the intensityof the 0 0 12 diffraction peak (peak area), I(0 0 12), to the intensityof the 1 1 0 diffraction peak (peak area), I(1 1 0), is I(0 012)>I(110).

In one embodiment of the present invention the TiCO, TiCNO, AlTiCO orAlTiCNO sublayer comprises protrusions, wherein the protrusions arecrystalline.

In one embodiment of the present invention said protrusions comprise atleast one twin boundary, preferably the protrusions share a (111) planeand are extended in its <211> direction. In one embodiment the crystalstructure of said protrusions are cubic.

In one embodiment of the present invention the length of saidprotrusions in its extended direction is 10-100 nm.

In one embodiment of the present invention the height of saidprotrusions as measured in a direction perpendicular to the surfacenormal of the substrate is less than a period of the multilayer,preferably less than 80% of the period of the multilayer, morepreferably less than or equal to 50% of the period of the multilayer.

The protrusions are considered to be important for the adhesion betweenthe sublayers of the α-Al₂O₃-multilayer. A good adhesion is necessary towithstand the high wear during cutting operations.

A high orientation throughout the α-Al₂O₃-multilayer is consideredimportant to provide the high flank and crater wear resistance. The highdegree of orientation of one α-Al₂O₃-sublayer of the α-Al₂O₃-multilayeris continued through a TiCO, TiCNO, AlTiCO or AlTiCNO sublayer.

The average height of said protrusions is preferably less than a periodof the α-Al₂O₃-multilayer. The wear resistance of the α-Al₂O₃-multilayerwill decrease if the α-Al₂O₃-sublayer is not continuous.

In one embodiment of the present invention the average thickness of saidα-Al₂O₃ sublayer is 40-800 nm, preferably 80-700 nm, more preferably100-500 nm or 100-300 nm. The α-Al₂O₃ sublayer should be of a sufficientthickness to provide a high wear resistance but small enough to providethe advantages of a multilayer. If the α-Al₂O₃ sublayer is of a toolarge thickness it will appear as a single layer without the advantagesof being a multilayer. The α-Al₂O₃-multilayer of the present inventionprovides a high resistance against flaking at plastic deformation of thecutting edge and a higher resistance to plastic deformation of thecutting edge as compared to a coating with a single α-Al₂O₃-layer.

In one embodiment of the present invention the coated cutting toolcomprises a first α-Al₂O₃-layer located between the substrate and theα-Al₂O₃-multilayer, wherein the thickness of said first α-Al₂O₃-layer is<1 μm, preferably <0.5 μm, more preferably <0.3 μm or 100-300 nm. It hasbeen found that the first α-Al₂O₃-layer located between the substrateand the α-Al₂O₃-multilayer is important to provide a high resistanceagainst flaking at plastic deformation of the cutting edge. In oneembodiment the first α-Al₂O₃-layer is of the same thickness as one ofthe α-Al₂O₃-sublayers of the α-Al₂O₃-multilayer.

In one embodiment of the present invention the coated cutting toolcomprises at least one layer of TiC, TiN, TiAlN or TiCN located betweenthe substrate and the α-Al₂O₃-multilayer, preferably TiCN. In oneembodiment of the present invention the thickness of the TiC, TiN, TiAlNor TiCN layer is 2-15 μm.

In one embodiment of the present invention the outermost layer of thecoating is an α-Al₂O₃ layer. Alternatively, one or more further layerscan cover the α-Al₂O₃ layer, such as layers of TiN, TiC, Al₂O₃ and/orcombinations thereof. In one embodiment of the present invention saidone or more further layers covering the α-Al₂O₃ layer is/are removedfrom the flank face or the rake face or the cutting edge or combinationsthereof.

In one embodiment of the present invention the substrate is of cementedcarbide, cermet, ceramic, high speed steel or cBN. The substrate shouldhave hardness and toughness that suit the coating of the presentinvention.

In one embodiment of the present invention the substrate is of cementedcarbide comprising 3-14 wt % Co and more than 50 wt % WC. In oneembodiment of the present invention the substrate of the coated cuttingtool consists of cemented carbide comprising 4-12 wt % Co, preferably6-8 wt % Co, optionally 0.1-10 wt % cubic carbides, nitrides orcarbonitrides of metals from groups IVb, Vb and VIb of the periodictable, preferably Ti, Nb, Ta or combinations thereof, and balance WC.

In one embodiment of the present invention the substrate consists ofcemented carbide with a binder phase enriched surface zone. Thethickness of the binder phase enriched surface zone is preferably 5-35μm as measured from the surface of the substrate and towards the core ofthe substrate. The binder phase enriched zone has in average a binderphase content at least 50% higher than the binder phase content in thecore of the substrate. A binder phase enriched surface zone enhances thetoughness of the substrate. A substrate with a high toughness ispreferred in cutting operations such as turning of steel.

In one embodiment of the present invention the substrate consists ofcemented carbide with a surface zone essentially free from cubiccarbides. The thickness of the surface zone essentially free from cubiccarbides is preferably 5-35 μm as measured from the surface of thesubstrate and towards the core of the substrate. By “essentially free”means that no cubic carbides is visible in an ocular analyse of a crosssection in a light optical microscope.

In one embodiment of the present invention the substrate consists of acemented carbide with a binder phase enriched surface zone as disclosedabove in combination with a surface zone essentially free from cubiccarbides as disclosed above.

In one embodiment of the present invention the coating is post treatedby shot peening, blasting or brushing to release tensile stresses of theCVD coated layers and to reduce the surface roughness.

In one embodiment of the present invention the coated cutting toolcomprises a layer of TiCN located between the substrate and theα-Al₂O₃-multilayer and wherein said TiCN layer exhibits a texturecoefficient TC(hkl), as measured by X-ray diffraction using CuKαradiation and θ-2θ scan, defined according to Harris formula

${{TC}({hkl})} = {\frac{I({hkl})}{I_{0}({hkl})}\left\lbrack {\frac{1}{n}{\sum\limits_{n = 1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \right\rbrack}^{- 1}$

where I(hkl) is the measured intensity (integrated area) of the (hkl)reflection, I₀(hkl) is the standard intensity according to ICDD'sPDF-card No. 42-1489, n is the number of reflections, reflections usedin the calculation are (1 1 1), (2 0 0), (2 2 0), (3 1 1), (3 3 1), (4 20), (4 2 2) and (5 1 1) exhibits a TC(4 2 2)≥3, preferably 3.5.

In one embodiment of the present invention the coated cutting toolcomprises the following layers from the substrate and towards the outersurface of the coating: TiN, TiCN, α-Al₂O₃, an α-Al₂O₃-multilayer ofalternating sublayers of TiCO and sublayers of α-Al₂O₃.

In one embodiment of the present invention the the total coatingthickness is 7-25 μm and the α-Al₂O₃-multilayer comprises 10-150sublayers of α-Al₂O₃. The thickness of the α-Al₂O₃-multilayer ispreferably 3-15 μm. This multilayer is preferred in turningapplications.

In one embodiment of the present invention the the total coatingthickness is 2-9 μm and the α-Al₂O₃-multilayer comprises 5-70 sublayersof α-Al₂O₃. The thickness of the α-Al₂O₃-multilayer is preferably 1-5μm. This multilayer is preferred in milling or drilling applications

The coated cutting tools described herein can be subjected topost-treatments such as blasting, brushing or shot peening in anycombination. A blasting post-treatment can be wet blasting or dryblasting for example using alumina particles.

EXAMPLES

Exemplifying embodiments of the present invention will now be disclosedin more detail and compared to reference embodiments. Coated cuttingtools (inserts) were manufactured, analyzed and evaluated in cuttingtests.

Sample Overview

Cemented carbide substrates were manufactured utilizing conventionalprocesses including milling, mixing, spray drying, pressing andsintering. The sintered substrates were CVD coated in a radial CVDreactor of Ionbond Type size 530 capable of housing 10.000 half inchsize cutting inserts. The ISO-type geometry of the cemented carbidesubstrates (inserts) were CNMG-120408-PM. The composition of thecemented carbide of the samples Single A1, Multi A6, Multi A24, MultiA26, Multi A32, Multi A56, Multi A28u and Multi A40u was 7.2 wt % Co,2.9 wt % TaC, 0.5 wt % NbC, 1.9 wt % TiC, 0.4 wt % TiN and the rest WC.The composition of the cemented carbide of the samples Multi B38 andMulti B58 was 7.5 wt % Co, 2.9 wt % TaC, 0.5 wt % NbC, 1.9 wt % TiC, 0.4wt % TiN and the rest WC. An overview of the samples is shown in Table1.

TABLE 1 Sample overview Sample Coating layout above TiN + TiCN + bondinglayers Single A1 α-Al₂O₃ Multi A6 α-Al₂O₃/(TiCO + α-Al₂O₃)₆ Multi A24α-Al₂O₃/(TiCO + α-Al₂O₃)₂₄ Multi A26 α-Al₂O₃/(TiCO + α-Al₂O₃)₂₆ MultiA32 α-Al₂O₃/(TiCO + α-Al₂O₃)₃₂ Multi A56 α-Al₂O₃/(TiCO + α-Al₂O₃)₅₆Multi A28u α-Al₂O₃/(TiCO + α-Al₂O₃)₂₈ Multi A40u α-Al₂O₃/(TiCO +α-Al₂O₃)₄₀ Single B1 α-Al₂O₃ Multi B38 α-Al₂O₃/(TiCO + α-Al₂O₃)₃₈ MultiB58 α-Al₂O₃/(TiCO + α-Al₂O₃)₅₈

CVD Deposition

A first innermost coating of about 0.4 μm TiN was deposited on allsubstrates in a process at 400 mbar and 885° C. A gas mixture of 48.8vol % H₂, 48.8 vol % N₂ and 2.4 vol % TiCl₄ was used.

Thereafter an about 7-7.5 μm thick TiCN was deposited in two steps, aninner TiCN and an outer TiCN.

The inner TiCN was deposited for 10 minutes at 55 mbar at 885° C. in agas mixture of, 3.0 vol % TiCl₄, 0.45 vol % CH₃CN, 37.6 vol % N₂ andbalance H₂.

The outer TiCN was deposited at 55 mbar at 885° C. in a gas mixture of7.8 vol % N₂, 7.8 vol % HCl, 2.4 vol % TiCl₄, 0.65 vol % CH₃CN andbalance H₂.

On top of the MTCVD TiCN layer a 1-1.5 μm thick bonding layer wasdeposited at 1000° C. by a process consisting of four separate reactionsteps.

First a HTCVD TiCN was deposited at 400 mbar, using a gas mixture of 1.5vol % TiCl₄, 3.4 vol % CH₄, 1.7% HCl, 25.5 vol % N₂ and 67.9 vol % H₂.

The three next steps were all deposited at 70 mbar. In the first(TiCNO-1) a gas mixture of 1.5 vol % TiCl₄, 0.40 vol % CH₃CN, 1.2 vol %CO, 1.2 vol % HCl, 12.0 vol % N₂ and balance H₂ was used. The next step(TiCNO-2) used a gas mixture of 3.1 vol % TiCl₄, 0.63 vol % CH₃CN, 4.6vol % CO, 30.6 vol % N₂ and balance H₂. In the last bonding layer step(TiN) a gas mixture of 3.2 vol % TiCl₄, 32.3% vol % N₂ and 64.5 vol % H₂was used.

Prior to the start of the subsequent Al₂O₃ nucleation, the bonding layerwas oxidized for 4 minutes in a mixture of CO₂, CO, N₂ and H₂.

On all samples, an α-Al₂O₃-layer was deposited on top of the bondinglayer at 1000° C. and 60 mbar in two steps. The first step contained agas mixture of 1.2 vol % AlCl₃, 4.7 vol % CO₂, 1.8 vol % HCl and balanceH₂, and a second step contained a gas mixture of 1.2 vol % AlCl₃, 4.7vol % CO₂, 2.9 vol % HCl, 0.58 vol % H₂S and balance H₂.

On sample Single A1 this layer was grown to approximately 5 μm, onsample Single B1 to approximately 9 μm.

On samples Multi A6, Multi A24, Multi A26, Multi A32, Multi A56, MultiB38 and Multi B58 this layer were grown to approximately 1 μm.

On samples Multi A28u and Multi A40u this layer were grown toapproximately 0.2 and 0.1 μm, respectively.

An α-Al₂O₃-multilayer was deposited on samples Multi A6, Multi A24,Multi A26, Multi A32, Multi A56, Multi A28u, Multi A40u, Multi B38 andMulti B58 wherein a bonding sublayer of TiCO was alternated with asublayer of α-Al₂O₃. The TiCO sublayer was for all examples depositedfor 75 seconds. It was deposited at 1000° C. and 60 mbar in a gasmixture of 1.7 vol % TiCl₄, 3.5 vol % CO, 4.3 vol % AlCl₃ and 90.5 vol %H₂. The α-Al₂O₃ sublayer was deposited in two steps using identicalprocess parameters as for the bottom α-Al₂O₃ layer. The first step wasperformed for 2.5 minutes and the process time of the second step wasadjusted to reach the period thickness of the multilayer in eachsamples.

One period is equal to the sum of the thickness of one TiCO bondingsublayer and the thickness of one α-Al₂O₃ sublayer. The measurement ofthe period in the α-Al₂O₃-multilayers of the samples was made bydividing the total thickness of the α-Al₂O₃-multilayer with the numberof periods in the layer.

The thicknesses of the layers of the samples were studied in a lightoptical microscope and in an SEM and are shown on Table 2.

TABLE 2 Layer thicknesses TiN + TiCN + Multi α- Period in Total bondingSingle α- Al₂O₃ [μm] multiα- coating layer Al₂O₃ (TiCO + Al₂O₃ thicknessSample [μm] [μm] α-Al₂O₃)_(x) [μm] [μm] Single A1 9.1 5.1 — — 14.2 MultiA6 8.8 1 5.1 0.85 14.9 (X = 6)  Multi A24 8.7 1 5.0 0.21 14.7 (X = 24)Multi A26 9.0 1 4.9 0.19 14.9 (X = 26) Multi A32 8.9 1 4.4 0.14 14.3 (X= 32) Multi A56 8.9 1 4.3 0.077 14.4 (X = 56) Multi A28u 8.9 0.2 6.10.21 15.2 (X = 28) Multi A40u 9.3 0.1 5.1 0.13 14.5 (X = 40) Single B18.6 9.1 — — 17.7 Multi B38 8.7 1 8.3 0.21 18.0 (X = 38) Multi B58 8.9 17.9 0.14 17.8 (X = 58)

XRD Analyze Results

XRD analyses were made as disclosed in the method section above. No thinfilm correction was applied to the intensity data. The intensities ofthe peaks 110, 113, 024, 116, 0 0 12 and 0 1 14 originating from α-Al₂O₃for the samples are presented in Table 3 with the values normalized suchthat the intensity of 0 0 12 was set to 100%. The XRD diffractogram ofsamples Multi A28u and Single A1 are shown in FIGS. 12 and 13,respectively.

TABLE 3 XRD intensities originating from α-Al₂O₃ Sample I(110) I(113)I(024) I(116) I(0 0 12) I(0 1 14) Single A1 48.8 10.0 19.3 9.1 100.069.4 Multi A6 35.2 3.9 10.8 4.5 100.0 49.4 Multi A24 36.5 4.9 12.5 6.7100.0 61.7 Multi A26 40.5 2.8 12.1 5.2 100.0 48.9 Multi A32 48.8 5.514.0 5.3 100.0 51.7 Multi A56 56.0 4.4 18.1 7.9 100.0 46.9 Multi A28u33.5 4.6 12.9 5.7 100.0 51.4 Multi A40u 92.8 15.5 30.3 18.6 100.0 61.0Single B1 16.0 2.1 6.1 2.5 100.0 41.6 Multi B38 14.3 2.3 4.7 1.6 100.028.1 Multi B58 12.6 1.2 4.9 1.5 100.0 24.0

The TiCN layer located between the substrate and the α-Al₂O₃-singlelayer of sample Single A1 was studied in XRD. Subsequent to thin filmcorrection and correction for absorption in the single α-Al₂O₃-layer ofthe data, the TC values were calculated using Harris formula. Theresults are shown in Table 4.

Harris Formula:

${{TC}({hkl})} = {\frac{I({hkl})}{I_{0}({hkl})}\left\lbrack {\frac{1}{n}{\sum\limits_{n = 1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \right\rbrack}^{- 1}$

where I(hkl) is the measured intensity (integrated area) of the (hkl)reflection, I₀(hkl) is the standard intensity according to ICDD'sPDF-card No. 42-1489, n is the number of reflections, reflections usedin the calculation are (1 1 1), (2 0 0), (2 2 0), (3 1 1), (3 3 1), (4 20), (4 2 2) and (5 1 1).

TABLE 4 h k l TC(h k l) 2 2 0 0.2 3 1 1 2.0 4 2 2 3.5

A corresponding TiCN layer was also present in all the samples providedwith the α-Al₂O₃-multilayers. The XRD diffractograms of theα-Al₂O₃-multilayers indicate a broad 111 reflection seen at about 36.1°in the XRD diffractogram whereby it could be concluded that the originfor this reflection should be the TiCO sublayers. XRD signal from theTiCO sublayers and signals from the TiCN layer is difficult to separatein analyzing the layers since both the TiCO and the TiCN are cubic withsimilar cell parameters. To analyze the TiCN layer theα-Al₂O₃-multilayers should first be removed by mechanical or chemicalmeans such as etching or polishing. Thereafter the TiCN layer can beanalyzed.

STEM

In order to investigate the protrusions of the sublayer, HAADF STEManalysis was made in a monochromated, aberration probe corrected Titan80-300 TEM/STEM.

Specimens were prepared in accordance with the method disclosed in themethod section above. Several protrusions of the TiCO sublayer in theα-Al₂O₃-multilayer were studied with STEM. The protrusions were handledas of cubic crystal structure and were aligned along its zone axis 011.It was found that the protrusions comprised a twin boundary. The twinboundary was a 111 plane and the protrusion was extended in its <211>direction. HAADF STEM images of sample Multi A32 are shown in FIGS. 10and 11.

Wear Tests

A blasting was performed on the rake faces of the coated cutting toolsprior to the wear tests. The blaster slurry used consisted of 20 vol-%alumina in water and an angle of 90 deg. between the rake face of thecutting insert and the direction of the blaster slurry. The pressure ofthe slurry to the gun was 1.8 bar for all wear tested samples.

PD Impression

The samples were tested in a dry turning test cutting in work piecematerial SS2541 (a 700×180 mm bar). Face turning was applied on said barfrom a diameter of 178 mm to a diameter of 60 mm. The following cuttingdata was used:

Cutting speed, V_(c): 200 m/min

Feed, f_(z): 0.35 mm/revolution

Cutting depth, a_(p): 2 mm

The stop criterion was defined as when the flank wear (Vb)≥0.5 mm or atedge breakage. The flaking is considered to occur mainly due to plasticdeformation of the cutting edge. Each insert edge was inspected aftereach 5 cuts and the flank wear on the main edge and on the secondaryedge was measured. When the flank wear reached a value of 0.4 mm thecutting edge was inspected after each 3 cuts.

The number of cuts at Vb=0.3 mm (an interpolated value) and the numberof cuts before flaking due to plastic deformation of cutting edge inrelation to the total number of cuts when stop criterion was reached isshown in Table 5.

TABLE 5 Number of cuts at Number of cuts when Vb = 0.3 Total numberflaking of coating was Sample mm of cuts observed Single A1 43.33 58 58Multi A6 45.00 61 58 Multi A24 46.67 58 50 Multi A26 53.57 73 55 MultiA32 45.00 64 50 Multi A56 47.50 64 45 Multi A28u 50.83 64 >64 (noflaking observed at end of test) Multi A40u 52.22 67 >67 (no flakingobserved at end of test)

It was concluded that the samples Multi A28u and Multi A40u were thesamples that did show the highest resistance to flaking in this test andthat all the multilayered samples showed a higher flank wear resistanceas compared to the reference Single A1.

PD Depression

The samples were tested in longitudinal turning at dry conditions in awork piece material SS2541 (a 700×180 mm bar). The following cuttingdata was used:

Cutting speed, V_(c): 98 or 110 m/min

Feed, f_(z): 0.7 mm/revolution

Cutting depth, a_(p): 2 mm

Time in cut: 30 s

Before starting the test, the insert was placed in a fixture and theposition of the cutting edge on the nose is set to zero via a dialgauge. After 30 seconds cutting time the new position of the cuttingedge on the nose was measured by the dial gauge giving a value of theedge depression. The worn edges were studied in a light microscope andthe degree of flaking in relation to the reference sample A1 was noted.The average results of 3 parallel pd-depression cutting test are shownin Table 6.

TABLE 6 Judgement Edge depression Edge depression of flaking [μm] [μm]in relation Sample (98 m/min) (110 m/min) reference Single A1 33 41Reference Multi A6 38 41 Worse Multi A24 31 35 Similar Multi A26 27 32Better Multi A32 31 35 Similar Multi A56 30 36 Similar Multi A28u 29 31Better Multi A40u 30 35 Better

It was concluded that the sample Multi A6 did not resist this cuttingtest better than the reference Single A1, while all the other samplesdid perform similar or better.

While the invention has been described in connection with variousexemplary embodiments, it is to be understood that the invention is notto be limited to the disclosed exemplary embodiments, on the contrary,it is intended to cover various modifications and equivalentarrangements within the appended claims.

Furthermore, it should be recognized that any disclosed form orembodiment of the invention may be incorporated in any other disclosedor described or suggested form or embodiment as a general matter ofdesign choice. It is the intention, therefore, to be limited only asindicated by the scope of the appended claims appended hereto.

1. A coated cutting tool comprising: a substrate; and a coating, whereinthe coating comprises an α-Al₂O₃-multilayer consisting of alternatingsublayers of α-Al₂O₃ and sublayers of TiCO, TiCNO, AlTiCO or AlTiCNO,said α-Al₂O₃-multilayer including at least 5 sublayers of α-Al₂O₃,wherein a total thickness of said α-Al₂O₃-multilayer is 1-15 μm, andwherein a period in the α-Al₂O₃-multilayer is 50-900 nm, wherein theα-Al₂O₃-multilayer exhibits an XRD diffraction over a θ-2θ scan of20°-140°, wherein a relation of an intensity of the 0 0 12 diffractionpeak (peak area), I(0 0 12), to intensities of the 1 1 3 diffractionpeak (peak area), I(1 1 3), the 1 1 6 diffraction peak (peak area), I(11 6), and the 0 2 4 diffraction peak (peak area), I(0 2 4), is I(0 012)/I(1 1 3)>1, I(0 0 12)/I(1 1 6)>1 and I(0 0 12)/I(0 2 4)>1.
 2. Thecoated cutting tool of claim 1, wherein an intensity of the 0 1 14diffraction peak (peak area), I(0 1 14), to the intensity of the 0 0 12diffraction peak (peak area), I(0 0 12), is I(0 1 14)/I(0 0 12)<2. 3.The coated cutting tool of claim 1, wherein a relation of the intensityof the 1 1 0 diffraction peak (peak area), I(1 1 0), to the intensitiesof the 1 1 3 diffraction peak (peak area), I(1 1 3), and the 0 2 4diffraction peak (peak area), I(0 2 4), is I(110)>each of I(113) andI(024).
 4. The coated cutting tool of claim 1, wherein the relation ofthe intensity of the 0 0 12 diffraction peak (peak area), I(0 0 12), tothe intensity of the 1 1 0 diffraction peak (peak area), I(1 1 0), isI(0 0 12)>I(110).
 5. The coated cutting tool of claim 1, wherein theTiCO, TiCNO, AlTiCO or AlTiCNO sublayer include protrusions, whereinsaid protrusions are crystalline.
 6. The coated cutting tool of claim 5,wherein said protrusions have at least one twin boundary, and whereinthe protrusions share a (111) plane and are extended in a <211>direction.
 7. The coated cutting tool of claim 5, wherein a length ofsaid protrusions in an extended direction is 10-100 nm.
 8. The coatedcutting tool of claim 5, wherein a height of said protrusions asmeasured in a direction perpendicular to a surface normal of thesubstrate is less than a period of the multilayer.
 9. The coated cuttingtool of claim 1, wherein an average thickness of said α-Al₂O₃ sublayeris 40-800 nm.
 10. The coated cutting tool of claim 1, further comprisinga first α-Al₂O₃-layer located between the substrate and theα-Al₂O₃-multilayer, in direct contact with the α-Al₂O₃-multilayer,wherein the thickness of said α-Al₂O₃-layer is <1 μm.
 11. The coatedcutting tool of claim 1, further comprising at least one layer of TiC,TiN, TiAlN or TiCN located between the substrate and theα-Al₂O₃-multilayer.
 12. The coated cutting tool of claim 11, wherein athickness of the TiC, TiN, TiAlN or TiCN layer is 2-15 μm.
 13. Thecoated cutting tool of claim 1, wherein an outermost layer of thecoating is an α-Al₂O₃ layer.
 14. The coated cutting tool of claim 1,wherein the substrate is cemented carbide, cermet, ceramic, high speedsteel or cBN.
 15. The coated cutting tool of claim 1, wherein thesubstrate is cemented carbide comprising 3-14 wt % Co and more than 50wt % WC.
 16. The coated cutting tool of claim 8, wherein the surfacenormal of the substrate is less than 80% of the period of themultilayer.